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Portosystemic Shunt

A healthy, soundly structured, and properly functioning liver is an indispensable component of the feline anatomy. Among the critically important roles performed by this large, reddish-brown organ is the detoxification of the blood that flows into it before being circulated to the heart and subsequently throughout a cat’s system.

It is the liver’s ability to filter out—or at least reduce the potency of—potentially poisonous compounds and infectious agents from circulating blood that prompts Dr. Richard Goldstein, DVM, associate professor of small animal medicine at Cornell University’s College of Veterinary Medicine, to characterize this organ as “the guardian of a cat’s body.” Unfortunately, Dr. Goldstein explains, some cats are born with a liver defect called portosystemic shunt, which can severely undermine the vital process of detoxification.

Normal detoxification depends on the fluent passage of blood that contains nutrients as well as toxins from the intestines into the liver via a relatively large conduit called the portal vein. In the normal liver, explains Dr. Goldstein, the blood is detoxified. “Toxic substances are either gotten rid of or changed so that they are friendly to the body,” he explains, “after which the cleansed blood flows back to the heart and is then circulated systemically.”

In portosystemic shunt, however, the toxic blood is unable to flow from the intestines into the liver because, in an affected cat, the portal vein does not lead into that organ. Instead, this large duct is connected to another blood vessel that bypasses the liver and leads directly to the heart. The circulating blood that has thus been diverted (shunted) around the liver and has moved directly to the heart without being properly detoxified will then be circulated throughout the affected animal’s body. These shunts are often the result of embryonic blood vessels that have failed to close, or from blood vessels that are not normally present in the fetus that bypass the liver.

The impact on a cat’s overall health resulting from the presence of elevated toxin levels in the uncleansed circulating blood can lead to a wide array of serious and in some cases life-threatening conditions, including neurologic and behavioral abnormalities, gastrointestinal disturbances, urinary tract disorders, and stunted growth. A majority of affected animals will experience digestive system abnormalities, such as diminished appetite, lethargy, weight loss, increased thirst, vomiting, diarrhea, and the development of bladder stones. The most frequently observed indications of the condition are such central nervous system signs as hyperactivity, disorientation, temporary blindness, and excessive salivation.

Early diagnosis of portosystemic shunt is crucially important in determining the outcome of the condition, explains Dr. Goldstein. The diagnostic measures will rely essentially on blood chemistry analysis, but are quite likely also to include abdominal ultrasound and x-rays. In addition, exploratory abdominal surgery may be required.

In some cases, he notes, dietary management, relying largely on a low-protein regimen, can help alleviate some of the clinical signs of this condition. Lowered protein in the diet will help to reduce nitrogenous metabolites that can lead to ammonium formation. Ammonium in the blood can cross into the brain and can cause neurologic signs such as seizures. Lactulose can bind ammonium in the gi system, and prevent its absorption into the blood. In addition, antibiotics such as neomycin can reduce ammonium producing bacteria. Alternatively, surgical management, which entails tying-off the shunting vessel and redirecting the flow of blood from the gastrointestinal tract into the liver, is often a preferable option, although some patients may require a second surgery to completely block the shunt. In any case, notes Dr. Goldstein “If the condition is recognized early, most cases of portosystemic shunt can be treated successfully by surgical closure.”